In a prior-art internal combustion engine with a V-type cylinder arrangement, banks or rows of power cylinders are inclined from each other through an angle of, for example, 90 degrees about the axis of rotation of a crankshaft. The crankshaft of such an internal combustion engine is provided with balancing weights to eliminate residual unbalanced forces of inertia from reciprocating masses of piston and connecting-rod assemblies. The balancing weights thus provided on the crankshaft are, however, not capable of eliminating the linear components of the residual unbalanced inertial forces even when the power cylinders of each bank or row of the engine are arranged to partake of the same crankpin.
Even if the angle set between the two banks of power cylinders is reduced to be less than 90 degrees with a view to providing compact construction of the engine, vibrations due to the residual unbalanced inertial forces could not be eliminated satisfactorily. The vibrations originating in the engine are thus transmitted to the body structure of the motorcycle without being dampened.